The conventional hydraulically-actuated, electronically-controlled fuel injection apparatus is disclosed in, for example, Published Japanese translations of PCT international publication No. 511527/1994. The injector used in the prior fuel injection apparatus has the structure, for example, shown in FIG. 13, which may control in a variable manner the fuel flow characteristics of the hydraulically-actuated injector in the fuel injection stroke of the engine and make possible the quick starting of the engine.
Referring to FIG. 13, the prior injector 1 has comprised of a main body having a central passage and fuel injection holes 13, and a casing 6 arranged so as to form an annular clearance for a fuel chamber 20 around the main body. The main body of the injector 1 comprises a nozzle body 2 formed with a central passage 49 and injection holes 13, a fuel supply body, or plunger barrel 5 forming an intensified chamber 7, a spacer body 81 and an annular spacer body 21 arranged between the nozzle body 2 and fuel supply body 5, the annular spacer body being provided therein with a bore 29, an injector body 4 provided with a pressure chamber 8 supplied with hydraulically actuating fluid, and a solenoid body 3 having therein a solenoid valve 16, the solenoid body being provided with a leak line of a draining groove 39 and a draining passage 38. The casing 6 surrounds all of the nozzle body 2, spacer body 81, annular spacer body 21 and fuel supply body 5 so as to provide the fuel chamber 20 between them and itself, the casing 6 being further secured to the injector body 4 to thereby keep the bodies in integration. The casing 6 is engaged in a fluid-tight manner at its one end with a stepped abutment 14 of the nozzle body 2 and also sealed at its other end against the injector body 4 by screw-fitting at a threaded face 80 thereof. The casing 6 has fuel inlet 11 and fuel outlet 12, both of which open to a common fluid supply rail 51 from which the fuel is constantly applied to the fuel chamber 20.
The injector 1 comprises an intensified chamber 7 provided in the fuel supply body 5 for intensifying the fuel fed from the fuel chamber 20, a fuel pass 22 formed through the spacer body 81, annular spacer body 21 and nozzle body 2 to supply the fuel from the intensified chamber 7 to the injection holes 13. The injection 1 further includes a needle valve 23 held for sliding movement in the central passage 46 in the nozzle body 2 so as to open the injection holes 13 by the action of the fuel pressure, a boosting piston 109 for applying pressure to the fuel in the intensified chamber 7, the pressure chamber 8 being supplied with hydraulically actuated fluid for applying the high pressure to the axial end of the boosting piston 109, and the solenoid actuated control valve 16 controlling the supply of the hydraulically actuated fluid into the pressure chamber 8.
Arranged in the bore 29 in the annular spacer body 29 is a return spring 18 to forcibly urge the needle valve 23 towards a closed position where the injection holes 13 are closed. The return spring 18 is abutted at its one end against the top of the needle valve 23 and at its the other end against the spacer body 81. The injector body 4 is provided therein with a concave 26 larger in diameter for forming a spring chamber 30 defined between opposing end faces of the fuel supply body 5 and an enlarged diameter portion 115 of a boosting piston 109. The spring chamber 30 contains therein a return spring 17 to forcibly urge the boosting piston 109 towards the pressure chamber 8. Arranged in a hollow 85 in the injector body 4 is a return spring 19 to normally bias the solenoid valve 16 towards a position where the flow of the hydraulically actuating fluid is shut off. The spring chamber 30 having the boosting piston 109 therein communicates with the fuel chamber 20 through a passageway 83 having a non-return valve 84 therein. Although the spring chamber 30 normally allows the entry of leakage fuel under the pressure equal with that in the fuel chamber 20, reciprocating movement of the boosting piston 109 forcibly displaces inflow fuel from the spring chamber 30 with the formation of a space.
The boosting piston 109 comprises a radially-reduced portion 114 forming a plunger having the bottom face to define partially the intensified chamber 7, and the radially-enlarged portion 115 arranged for reciprocating movement in the concave 26 in the injector body 4 and provided with the top face to define partially the pressure chamber 8. The boosting piston further includes a guide ring portion 118 depending from the periphery of the enlarged portion 115 so as to form a sliding surface 49 for linear movement in contact with the inner surface of the concave 26. The ring portion 118 is to ensure the steady reciprocating movement of the boosting piston 109. While the reduced portion 114 of the boosting piston 109 is arranged in a radially-reduced bore 42 for reciprocating movement, the enlarged potion 115 is arranged in the concave 26 in the fuel supply body 5. Provided in the concave 26 in the injector body 4 is a sealing member 44 of a rubber-made O ring for sealing up a clearance between the boosting piston 109 and the concave 26 to prevent leakage of the hydraulically-actuating fluid in the pressure chamber 8 into the spring chamber 30, resulting in blockage between the spring chamber 30 and pressure chamber 8. The return spring 17 is arranged between the fuel supply body 5 and the boosting piston 109 in compression. The reduced portion 114 and the enlarged portion 115 are formed separately from each other and the top face 116 of the reduced portion 114 is abutted against the enlarged portion 115 at its inner surface.
The intensified chamber 7 is defined at an end of the radially-reduced bore 42 in the fuel supply body 5 and supplied with the fuel from the fuel chamber 20 through a fuel passageway 37 in the annular spacer body 21 and a fuel passageway 35 in the spacer body 81. The fuel passageway 35 provided with a non-return valve 36 for checking a backward flow of pressurized fuel in the intensified chamber 7 to the fuel chamber 20. Fuel under pressure in the intensified chamber 7 is supplied to the injection holes 13 through the fuel passes 22 in the spacer body 81, annular spacer body 21 and nozzle body 2. High hydraulic pressure in fuel acts on tapered faces 45 and 45a on the needle valve 23 to hydraulically lift the needle valve 23 that is held in the central passage 46 in the nozzle body 2 for linear sliding movement. As a result, the fuel pressure makes a fuel flow between the nozzle body 2 and the needle valve 23 and opens up the nozzle holes 13.
The boosting piston 109 is provided with an annular stepped face 73 that is contoured in exposure to the pressure chamber 8 by planing down the periphery of the top surface 75 of the enlarged portion 115. A surface of the injector body 4 exposed to the pressure chamber 8 is formed in a flat face 72 which is in parallel with the top surface 75 of the boosting piston 109. It will be noted that an annular narrowed clearance 74 for the pressure chamber 8 may be provided between the opposed faces 72 and 73 of the injector body 4 and the boosting piston 109. The boosting piston 109 is forcibly abutted at its central rise against the flat face 72 of the injector body 4 by the action of the return spring 17.
In this prior injector 1, the spring chamber 30 having the return spring therein is defined in the radially-enlarged concave 26 that is formed in the injector body 4 for the linear sliding movement of the enlarged portion 115 and guide ring portion 118 of the boosting piston 109. The sealing member 44 interposed between the enlarged portion 115 and the concave 26 is to seal up the peripheral sliding surface 49 of the boosting piston 109, which may is in sliding contact with the concave 26, resulting in prevention of fuel leakage from the spring chamber 30 into the pressure chamber 8. The fuel in the boosting chamber 7 is allowed to invade the spring chamber 30 through a small clearance around the reduced portion 114 for a plunger, or the sliding surface 43 of the reduced portion 114 in contact with the radially-reduced bore 42 of the fuel supply body 5. The fuel in the fuel chamber 20 is also allowed to invade the spring chamber 30 through a clearance between the opposed surfaces of the injector body 4 and the fuel supply body 5, which are abutted against each other. It is to be noted that the spring chamber 30 is normally provided with a cavity equivalent with a stroke of the boosting piston 109. On the fuel in the spring chamber 30 increasing to the level where the cavity in the spring chamber 30 is reduced in volume less than the stroke of the boosting piston 109, the fuel in the spring chamber 30 is discharged to the fuel chamber 20 through passageway 83 having the non-return valve 84.
The return spring 17 is arranged between a spring retainer 117 and the top face of the fuel supply body 5 in compression so as to make the reduced portion 114 follow the movement of the enlarged potion 115. The top 116 of the reduced portion 114 abutted against the enlarged portion 115 is designed in the form of a convex.
Disclosed in FIG. 12 is a prior engine fueling system for an internal combustion engine having incorporated with the injector 1. The engine fueling system includes the injectors 1 each assigned to a cylinder and connected to a common fuel supply rail 51, which is supplied with fuel from a fuel tank 52 through a fuel filter 54 by the driving of fuel pump 53. The common fuel supply rail 51 communicated with the injectors 1 is connected to the fuel tank 52 through a fuel recovery line 55. It will be understood that the injectors 1 is constantly supplied with the fuel of the required pressure at the fuel inlets 11 and fuel outlets 12 through the common fuel supply rail 51.
The injector 1 is designed so as to feed hydraulically actuating fluid, or high-pressurized oil, to the intensified chamber 8 for applying the boosting pressure to the fuel. The injectors 1 are communicated to a high-pressure fluid manifold 56, to which the fluid in a fluid reservoir 57 is fed through a fluid supply line 61 by the driving of a fluid pump 58. There are provided a fluid cooler 59 and a fluid filter 60 in the fluid supply line 61. The fluid supply line 61 is branched into a lubricant line 67 communicating with an oil gallery and a hydraulic fluid line 66 communicated with a hydraulic pump 63. A flow control valve 64 is to regulate the fluid supply to the high-pressure fluid manifold 56 from the hydraulic pump 63 through the hydraulic fluid line 66. A controller unit 50 is designed so as to control both of the flow control valve 64 and solenoids 10. The controller unit 50 is applied with data indicative of the performance of an engine, that is, rotational frequencies detected by a rotational frequency sensor 68, throttle valve openings detected by a accelerometer 69 and crankshaft angles detected by a crank angle sensor 70 crank travel crankshaft revolutions valve openings. The controller unit 50 is also input with a hydraulic pressure at a pressure sensor 71 in the high-pressure fluid manifold 56.
The solenoid 10 is to actuate needle valves 23 for opening and closing the nozzle holes 13. Now referring to FIG. 3, energizing the solenoid 10 under favor of an instruction from the controller unit 50 attracts an armature 32, causing lifting the solenoid valve 16 against the return spring 19. Lifting the solenoid valve 16 results in separation of a tapered surface 86 of the solenoid valve 16 from a valve seat 87 of the injector body 4 to thereby make an annular clearance 33 for admitting the hydraulic-actuating fluid into the pressure chamber 8 from the high-pressure fluid manifold 56 through a fluid inlet port 31 and fluid passageway 34 in the injector body 4. The hydraulically actuating fluid applied into the pressure chamber 8 fills up the annular clearance 74 defined between the top surface 75 of the enlarged portion 115 of the boosting piston 109 and the flat face 72 of the injector body 4 to thereby act on the boosting piston 109. Meanwhile, the fuel in the common fuel supply rail 51 is fed into the fuel chamber 20 through the fuel inlet 11 in the casing 6, and then supplied into the intensified chamber 7 from the fuel chamber 20 through both of the fuel passageway 37 in the annular spacer body 21 and the fuel passageway 35 in the spacer body 81.
With the boosting piston 109 moving downwards under the action of the hydraulically actuating fluid, the non-return valve 36 shuts off the fuel passageway 35 to hydraulically intensifying the fuel in the intensified chamber 7. As a result, the hydraulic pressure in the fuel acts on the tapered faces 45, 45a on the needle valve 23 to cause the lifting of the needle valve 23 against the return spring 18. Electro-magnetically de-energizing the solenoid 10 causes downward movement of the solenoid valve 16 by the action of the return spring 19 to thereby open the draining grove 39 for discharging the hydraulically actuating fluid out of the pressure chamber 8 through the draining grove 39 and the draining passage 38. Following such discharge of the hydraulically actuating fluid out of the pressure chamber 8, the boosting piston 109 may return to its home position under favor of the return spring 17 to make the intensified chamber 7 substantially equal in pressure with the fuel chamber 20. Reduction in the fuel pressure on the needle valve 23 causes seating the tapered face 45 in contact with the valve seat of the nozzle body 2 by the action of the return spring 18 to thereby close the nozzle holes 13.
The prior injector 1 of the type described above has the disadvantage such that, since work to be done on intensifying the fuel by the boosting piston 109 is partially consumed in work done on opening the non-return valve 84 for exhausting the fuel, the fuel injected 1 may lack in amount, or the output may become sufficient, resulting in adverse variations in the amount of injected fuel for each injection cycle or each cylinder, that is, in the rotation of the output shaft in the engine.
Instead of the passageway 83 and the non-return valve 84 employed in the prior injector 1 shown in FIG. 13, this applicant has already filed the co-pending application, refer to Japanese Patent Application No. 46830/1996, to propose an injector 90. Referring to FIG. 14, the injector 90 has a sealing member 47 of rubber-made O ring provided in contact with the sliding surface 43, and a relief port 40 for opening the concave 26 to the atmosphere. According to the proposed injector, there is no invasion of fuel into the concave 26 with the result of no requirement of discharging the fuel invaded. It has become capable of no loss in work done on intensifying by the boosting piston 109 with full efficiency of the intensifying power. In comparison with the injector 1, the injector 90 shown in FIG. 14 is of the s ame construction as the injector 1 with the exception of the provision of the sealing member for preventing leakage of fluid into the concave 26, instead of the discharging of fluid invaded into the concave 26. In the following description, the same reference character identifies equivalent or same parts and the repetition of the same parts is omitted.
In accordance with the injector having the boosting piston 109 described above, the hydraulically actuating fluid in the pressure chamber 8 acts on the boosting piston 109 that intensifies in the intensified chamber 7 the hydraulic pressure with a magnifying in proportion to the surface ratio of the enlarged portion 115 with the reduced portion 114 to thereby forcibly inject the fuel out of the nozzle holes 13 at the tip of the injector. The injectors shown in FIGS. 13 and 14 are identical in that the sealing member of resin-made O ring may separate the intensified chamber from the pressure chamber for preventing the hydraulically actuating fluid and the fuel from contamination with each other. In the injector 1 in FIG. 13, the sealing member 44 of rubber-made O ring is arranged between the concave 26 and the sliding surface 49 of the enlarged portion including the guide ring portion 118 and the leaked fuel in the spring chamber 30 is expelled to the fuel chamber 20 through the passage 83. On the other hand, the injector 90 in FIG. 14 has the sealing member 47 of rubber-made O ring arranged between the relatively sliding surfaces 43 of the radially reduced bore 42 and the reduced portion 114 of the boosting piston 109, and the relief port 40 for opening the spring chamber 30 to the atmosphere in the engine cover.
However, the boosting piston 109 makes the reciprocating movement with high speed for each of injection cycles and thus the sealing members 44, 47 are apt to be subject to deterioration due to abrasion. The applicant has found that even the improved injector proposed by this applicant and shown in FIG. 14 involves the following shortcomings to be eliminated. The extremely high pressure in the intensified chamber 7 may act in the form of impulse waves on the sealing member 47 which is arranged between the relative sliding surfaces 43 of the radially reduced bore 42 and the reduced portion 114 of the boosting piston 109. Such impulse force causes cavitation in the vicinity of the sealing member 47 so that the sealing member 47 of rubber-made O ring get rough at its surface, resulting in adverse reduction in the sealing performance. Deterioration of the sealing member 47 in sealing performance may permit the invasion of fuel from the intensified chamber 7 along the relative sliding surface 43 into concave 26, or the spring chamber 30, from which the fuel is expelled into the cylinder head cover through the relief port 40. There is thus such fear that the contamination of lubricating oil with fuel makes adverse operating conditions of engines such as decrease in viscosity of lubricating oil, insufficient lubrication in engine, destruction of engine parts due to overheating or the like. Contamination of fuel with lubricating oil vice versa causes a danger of making worse the exhaust gases, or increasing the smoke.
An object of the present invention is to overcome the above-described shortcomings to be solved, and to provide an injector in which the leakage of an intensified fuel along relatively sliding surfaces of a concave and a radially enlarged portion or a radially reduced portion of a boosting piston is prevented by sealing members that is provided between the relatively sliding surfaces, the improved injector wherein the sealing members are protected from the action of instantaneous, high-pressure impulses or dynamic high-pressure impulses, applied from a pressure chamber or intensified chamber, by means of blocking the high-pressure impulses on the sliding surfaces at a location between the sealing members and the pressure chamber or intensified chamber, or by means of releasing the high-pressure impulses from the sliding surfaces between the intensified chamber and the sealing members to a lower-pressure side of fuel.